Medical procedures to treat cardiovascular diseases are becoming less invasive in nature, such that a physician can insert a small medical device into a subject through a small incision and navigate the device through vasculature to the heart and the specific treatment site. One result is that the physician requires specialized tools to see where the device is travelling as well as the destination treatment location. Stereotactic navigation is the field of taking pre-acquired images of the anatomy of interest and using localization systems to track medical instruments with respect to the pre-acquired imaging. Stereotactic navigation requires position sensing capabilities to be able to locate and track the medical instruments within the human body and display the position with respect to other medical imagery like x-ray, CT, MRI, ultrasound, and electrocardiogram maps.
Current position sensing systems suffer from several issues. Position sensing systems need to provide flexibility to localize many different instruments based on physician preference, and accuracy in inhomogeneous tissues such as bone, air, blood, muscle, and fat, as those tissue characteristics change with breathing and heart beat. The balance of accuracy and flexibility is very difficult to achieve. Electromagnetic position sensing systems are often accurate systems because they do not depend on the tissue characteristics of the living body. However, electromagnetic systems are very proprietary in nature and require proprietary electromagnetic sensors embedded in every instrument used during the procedure that the physician needs to localize. Electrical-potential position sensing systems are typically very flexible in their ability to track different instruments in an open architecture manner using standard electrodes integrated into many medical instruments. However, the accuracy of electrical-potential systems is poor because they are susceptible to the varying tissue impedance changes due to breathing and heartbeat.
Attempts to combine the accuracy of electromagnetic localization and flexibility of electrical-potential localization have so far failed to provide a system that overcomes the issues of the separate systems. Current hybrid position sensing systems aim to calibrate a volume localized by electrical-potential localization to a volume localized by electromagnetic localization with a single instrument with respect to body surface electrodes and use that calibration to track other instruments in a common calibrated volume. However, any calibration of electromagnetic localization field to electrical-potential localization field calculated by the single instrument is valid only at a particular point in time correlated with a particular point in a breathing cycle and heart beat cycle or is an average over time that is not particularly accurate at any given single point in time. The result is a gated position sensing system that is only accurate periodically.
Thus, a need exists for improved systems and methods of localizing medical instruments within a subject during minimally invasive cardiovascular medical procedures.